And the thing you should notice here is that it's doing a lot of the same things over 2 1 and over again. So, for example, we'll see 2, 1 2 1 here. And 2, 1 here.

在这里你要注意的是,它不断在重复同样的工作,例如我们看这里的1,还有这里的。

麻省理工公开课 - 计算机科学及编程导论课程节选

Just like Fibonacci, it's doing the same work over and over again.

就像Fibonacci数列一样，他不断地重复相同的工作。

麻省理工公开课 - 计算机科学及编程导论课程节选